In hospitals containing many patients, it is common practice to preload hypodermic syringes and other vials in a hospital pharmacy and then store or immediately transfer them to the particular floors for injection into patients.
Many of the medicaments and diluents for modifying concentrations of medicaments are supplied to hospital pharmacies in bulk sterilized containers. The pharmacist transfers measured dosages from these bulk containers to a series of smaller syringes or vials.
Metering syringes to dispense a repeated measured dosage to such smaller containers have been proposed in the past. These have included expensive reusable metal housings with screw thread dosage regulators. These had to be cleaned and sterilized between usages with different sterile medicament and diluents. In addition to their expense, these prior metal housing type metering syringes required laborious screw threading to change the dosage setting. Also, there have been elaborate stop mechanisms to measure dosage that included extensive structure extending behind the thumb pressure area of the syringe. Some included long screw mechanisms coaxial with the syringe barrel. These were cumbersome to handle.
Recently it has been proposed to provide a disposable thermoplastic syringe with a double check valve system for dispensing repeated measured dosages of medicament for diluents. Since a conventional plastic disposable hypodermic syringe was connected to such double check valve system, it had small finger flanges, and also lacked a settable dosage stop mechanism. For each vial or syringe charged with medicament or diluent, the particular dosage had to be visually read from the calibrations of the conventional disposable plastic syringe.